Chapter 13 Alkenes Flashcards
what is an alkene
unsaturated hydrocarbon that can be aliphatic or alicyclic
what is the general formula of an alkene
CnH2n
what is the shape and bond angle for an alkene aroound one of the carbon atoms
trigonal planar
120
what are the bonds in each carbon atom in the alkene bond
3 sigma bonds
1 Pi bond
what is a Pi bond
Bond formed due to a sideways overlap of p orbitals
why do the carbons have a Pi bond
3 of the electrons in the p orbital overlap with the other atoms electrons to produce a sigma bond. This leaves one electron per carbon that are above and below the C-C sigma bond so produces a sideways overlap
what happens to the bonds when an alkene reacts
the Pi bond is weaker than the sigma bond so less energy is required to break it causing the electrons in the Pi bond to move away breaking the double bond
what is a Stereoisomer
Isomers of molecules with different arrangements in space that they take up
what two notations can be used to distinguish Stereoisomers
E/Z
cis/trans
which symbols can you use when the two priority groups are on the same side
cis-
Z-
which symbols can you use when the two priority groups are on opposite sides
trans-
E-
when do you use cis/trans
when one of the attached groups on each carbon atom is a hydrogen
when do you use E/Z
when one or either of the attached groups on at least one carbon atom is not a hydorgen
what is the Cahn-Ingold-Prelog (CIP) rules
Naming system for stereisomers that focuses on the atomic number of atoms attached to each carbon in the double bond
How does the CIP rules work
Find the atomic number of each atom attached to one carbon atom. The one with the highest number has priority. Then use the correct symbol based on the relative positions of the two priority atoms
why are Pi bonds weaker than sigma bonds
They are more exposed and spread out than sigma bonds
why are the Pi bonds useful for alkenes
they are why alkenes are far more reactive by turning the one of the carbon atoms into a carbocation allowing for electrophilic addition reactions
what happens during the electrophilic addition reaction for alkenes
> electrophilic atom is attracted to the alkene and bonds to one of the carbon atoms by taking the electrons from the Pi bond
this makes the other carbon a carbocation
The carbocation bonds to a negatively charged atom
what is a carbocation
Positively charged carbon ions that are highly reactive and very unstable
what Markownikoff’s rule
if you have a two step process with carbocation intermediate the preferred route is governed by the stability of the carbocation
what are the four carbocations
tertiary three C-C bonds most stable
secondary two C-C bonds
primary one C-C bond
methyl no C-C bonds
what is the word formula for the adddition of hydrohalides
Alkene + hydrohalide –> haloalkane
what is the word formula for the addition of halogens
Alkene + halogens –> dihaloalkanes
what is the word formula for the addition of steam
Alkene + steam –> Alcohol
